1. Field of the Invention
The present invention relates to an image display device, specifically an image display device which produces an image by joining a plurality of divided frames to generate a single frame. The present invention also relates to an image control device and method for correcting an image displayed on the image display device.
2. Description of the Related Art
Cathode ray tubes (CRTs) are widely used in image display devices such as television receivers or computer monitors. Inside a cathode ray tube, provided are an electron gun and a fluorescent screen. The electron gun produces an electron beam emitted toward the fluorescent screen. The electron beam scans to form a scanned image.
A cathode ray tube generally has a single electron gun. In recent years, however, a multiple-gun cathode ray tube, comprising two or more electron guns, has been developed. A multiple-gun cathode ray tube produces an image as follows. Each of the electron guns produces its own electron beam, and a plurality of divided frames are generated. The divided frames are joined to form a single frame. The related art concerning multiple-gun cathode ray tubes is disclosed in, for example, Publication of Examined Japanese Utility Model Application No. Sho 39-25641, Publication of Examined Japanese Patent Application No. Sho 42-4928 and Publication of Unexamined Japanese Patent Application No. Sho 50-17167. A multiple-gun cathode ray tube has several advantages of a smaller depth dimension and a larger screen, as compared to a single-gun cathode ray tube.
To achieve high picture quality throughout the entire screen of a multiple-gun cathode ray tube, it is desirable that the joint area of the divided frames is as inconspicuous as possible. The related art is, however, insufficient for making the joint area of the divided frames inconspicuous. Thus, there are no guarantees that the joint areas of the divided frames are always inconspicuous so as not to disturb watching.
Precision in joining a plurality of divided frames is influenced by, for example, xe2x80x98image distortionxe2x80x99, misconvergence, terrestrial magnetism or change of cathode ray tubes with time. Firstly, image distortion refers to a phenomenon in which an image displayed on a screen of a cathode ray tube appears distorted. Images usually appear distorted in a form of pincushion. The reason is that, since a screen of a cathode ray tube is generally rectangular, the distance traveled by the electron beam reaching the screen is the longest at each four corner of the screen.
The related art practice followed in minimizing image distortion is to optimize a deflection magnetic field generated by a deflection yoke. In recent years, however, image display devices have greater aspect ratios and flatter screens. This makes it impossible to correct image distortion completely only by a deflection magnetic field generated by a deflection yoke. There are several methods to correct image distortion which remains uncorrected by a deflection yoke. One example is to modulate a deflection current fed to a deflection yoke. But this method requires an additional circuit for modulation, which causes a problem of cost increase.
Second, description moves to misconvergence. A cathode ray tube for displaying color images produces electron beams for a set of primary colors for color display. In order to reproduce input signals accurately on the screen, the electron beams for respective colors have to converge on the screen. However, the electron beams for their respective colors are influenced by different magnetic fields from color to color and may fail to converge. This causes a phenomenon in which the positions where the electron beams strike the screen are deviated from each other. This phenomenon is called misconvergence.
Correction for misconvergence is made in a manner basically similar to the case of image distortion. That is, the electron beams for their respective colors are designed to converge throughout the entire screen by means of distribution of deflection magnetic fields generated by a deflection yoke itself. As in the case of image distortion, however, it is difficult to correct misconvergence completely only by distribution of magnetic fields.
The related art practice followed in correcting misconvergence which remains uncorrected by a deflection yoke is to move the electron beams for their respective colors separately by using an additional correction subyoke separate from a deflection yoke, thereby converging the electron beams accurately. This method requires not only a subyoke but an additional circuit for driving the subyoke, resulting in an increase in cost of manufacturing.
As described above, the related art adopts the method of correcting image distortion or misconvergence by using deflection magnetic fields. Adjustments for correction by using deflection magnetic fields involve spreading an image repeatedly to the entire screen in each of the horizontal direction and the vertical direction. This method therefore has some other undesirable aspects such as low worker efficiency and variations according to worker, which makes it difficult to effect optimal adjustment of image distortion constantly.
Another problem of the related art method is deterioration in resolution. Eliminating image distortion or misconvergence by using a deflection yoke also involves distorting deflection magnetic fields forcedly, which results in non-uniform magnetic fields. The distorted magnetic fields cause deterioration in focusing characteristics such as spotsize of an electron beam, resulting in deterioration in resolution.
The description given above has been made concerning the problems common to cathode ray tubes, such as image distortion, misconvergence and correction therefor. In the case of multiple-gun cathode ray tubes, these problems further influence precision in joining a plurality of divided frames. It is therefore desirable that, in the case of multiple-gun cathode ray tubes, image distortion or misconvergence is properly corrected and a plurality of divided frames are joined accurately so that the joint areas of the divided frames are inconspicuous.
Thirdly, cathode ray tubes are under influences of terrestrial magnetism or others. The influences of terrestrial magnetism or others vary according to the area of use and also cause image distortion. Image distortion due to terrestrial magnetism also exerts an undesirable influence on the display of the joint areas of the divided frames in the case of multiple-gun cathode ray tubes. Multiple-gun cathode ray tubes of the related art, however, are insufficient for display control of the joint areas in consideration of the area of use.
Lastly, image display performance of a cathode ray tube also deteriorates due to change of processing circuits such as a deflection circuit with time. Multiple-gun cathode ray tubes of the related art are also insufficient for display control of the joint areas in consideration of change with time.
Furthermore, correcting image distortion or misconvergence in a cathode ray tube in use and thereby joining a plurality of divided frames properly require that the magnitude of image distortion or misconvergence in a cathode ray tube in use be measured. As is the general practice in the related art, however, data for correction for image distortion or others is taken during manufacturing. Measurements in cathode ray tubes in use are rare.
The present invention has been made to overcome the foregoing problems. An object of the present invention is to provide an image control device and method, and image display device, capable of producing an image of high quality by joining a plurality of divided frames with the joint areas being inconspicuous.
An image control device of the invention comprises control means for performing control in such a manner that the unidimensional picture signal inputted to the image display device is converted into discrete two-dimensional image data, and for performing control in such a manner that an array of pixels in the image data is corrected based on the light or the electrical signal outputted from the position detecting means, so that the divided frames are joined properly and displayed when the image display device produces an image, and then the corrected image data is converted into a picture signal for display on the image display device and is outputted.
An image display device of the invention comprises: position detecting means provided at a position facing a joint area of the adjacent divided frames, for outputting light or an electrical signal in response to a status of display of the image; control means for performing control in such a manner that the picture signal inputted unidimensionally is converted into discrete two-dimensional image data, and for performing control in such a manner that an array of pixels in the image data is corrected based on the light or the electrical signal outputted from the position detecting means, so that the divided frames are joined properly and displayed when the image display device produces an image, and then the corrected image data is converted into a picture signal for display and is outputted; and image display means for producing an image based on the image data corrected by the control means.
An image control method of the invention involves: performing control in such a manner that the unidimensional picture signal inputted to the image display device is converted into discrete two-dimensional image data; and performing control in such a manner that an array of pixels in the image data is corrected based on the light or the electrical signal outputted from the position detecting means, so that the divided frames are joined properly and displayed when the image display device produces an image, and then the corrected image data is converted into a picture signal for display on the image display device and is outputted.
In the image control device and method, and an image control method, in the control means, control is performed in such a manner that the picture signal inputted unidimensionally is converted into discrete two-dimensional image data. Further, control is performed in such a manner that an array of pixels in the image data is corrected based on the light or the electrical signal outputted from the position detecting means, so that the divided frames are joined properly and displayed when an image is produced, and then the corrected image data is converted into a picture signal for display and is outputted. This control is accomplished as follows. Based on the light or the electrical signal outputted from the position detecting means, an operation for correcting the image data horizontally is performed, thereby a plurality of divided frames are joined properly in the horizontal direction and displayed. Further, an operation for correcting the image data vertically is performed.
The image display device of the invention further comprises position estimating means. The position estimating means obtains data on a pixel position in the joint area of the divided frames based on the light or the electrical signal outputted from the position detecting means, and estimates data on a pixel position in an area other than the joint area of the divided frames based on the obtained data. Further, the control means corrects the image data based on the estimated data, so that the divided frames are joined properly and displayed.
The position detecting means is mounted facing the overlap region of the frames. The position detecting means is therefore capable of detecting the position of an electron beam substantially in the overlap region of the frames. In the present invention, a pixel position in an area where no position detecting means is provided is estimated by the position estimating means. A pixel position in an area where no position detecting means is provided can be estimated and obtained in consideration of a certain tendency of image distortion in a CRT as shown in FIG. 17. This enables data required for joining a plurality of divided frames properly to be obtained throughout the entire screen as needed.
Other and further objects, features and advantages of the invention will appear more fully from the following description.